1. Field of the Invention
The present invention relates to a thin slide mechanism that can be incorporated in a portable electronic device such as a cellular phone, a PHS, and a PDA, and more particularly to a slide unit mechanism having high durability and reduced surface area of the internal slide structure that can be viewed from the outside.
2. Description of the Related Art
The so-called slide-type portable electronic device in which a main body portion and a monitor portion are divided into two layers of an upper layer portion and a lower layer portion and an operation portion located on the inner side of the lower layer portion is exposed by sliding the upper layer portion are presently well known.
In the conventional slide-type portable electronic device, a slide device is used in which one end of a torsion spring is fixedly attached to a first housing serving as the monitor portion and the other end is fixedly attached to a second housing serving as the main body portion and which is operated by using an elastic pressure of the torsion spring.
For example, Japanese Patent Publication No. 2004-253526 discloses a structure that has a first member and a second member and in which sliding movement is induced by inserting an engagement portion into a guide hole. In this structure, one end of a torsion spring is fixed to the engagement portion and the other end is fixed to the housing.
Further, Japanese Patent Publication No. 2007-224963 discloses a structure that includes a movable frame that is joined to both ends of a metallic plate and in which one end of a torsion spring is fixed to the inner side of the joining portion of the plate and the other end is fixed to the frame. International Patent Publication No. 2008-502175 discloses a structure that includes a frame movable on guide bars provided at both sides in the longitudinal direction and in which one end of a torsion spring is fixed to the frame and the other end is fixed to the frame on the inner side of the guide bars.
When a torsion spring is used in such portable electronic devices, a predetermined length is necessary in the sliding direction. Thus, when a housing is opened and closed by using a torsion spring, one end of the torsion spring should be fixedly attached close to the center of the slide length in order to generate a uniform spring force. For example, in the slide device described in Japanese Patent Publication No. 2007-224963, one end of each of two torsion springs is fixedly attached substantially close to the center of the housing. Therefore, a plate of a predetermined width is necessary to hide the internal slide structure where the torsion spring or the like is disposed.
Because a predetermined spring force is necessary to cause such device to slide, a specific limitation is placed on the possible reduction of the torsion spring in size. Therefore, it is necessary to provide a plate for hiding about half of the slide length.
Furthermore, because of a recent spread of oneseg portable devices, portable electronic devices has also been developed in which a horizontally long monitor is disposed at the housing and caused to slide in the widthwise direction. For example, Japanese Patent Publication No. 2007-267238 discloses a portable device in which sliding is induced in the widthwise direction.
Torsion springs are also used in such portable electronic devices in which sliding is induced in the widthwise direction. However, because the predetermined spring force is required, the arrangement zone of the torsion springs sometimes occupies more than half of the slide length, and therefore it is necessary to provide a plate having a large enough surface area to hide the slide. For this reason, a slide length is restricted so that the plate could not be seen from the outside of the portable device. As a result, the surface area of the lower layer portion (operation portion) that is exposed when the upper layer portion (monitor portion) is caused to slide is smaller. Therefore, the size and arrangement of operation buttons are restricted.
Further, in the conventional slide device using spirally wound springs or torsion spring, the width of the slide device is increased. As a result, possible arrangements of antenna in the monitor portion are limited in the portable electronic devices in which sliding is induced in the widthwise direction.
Further, when a spirally wound spring or a torsion spring of a conventional size is used, a predetermined space is necessary for separation between the diametrical direction of the spring and the plate that will be locked. Consequently, this space acts as a technical barrier to thickness reduction in portable electronic devices incorporating a slide unit.